diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index afdfcd2..0631f99 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,7 +7,7 @@ jobs:
           matrix:
             python-version: ['2.7','3.12']
         container:
-          image: python:${{ matrix.python-version }}
+          image: python:${{ matrix.python-version }}-slim
         runs-on: ubuntu-latest
         steps:
             - name: checkout repo content
diff --git a/train_arrival.py b/train_arrival.py
index 98b448a..cd0ed8c 100644
--- a/train_arrival.py
+++ b/train_arrival.py
@@ -62,7 +62,7 @@ def _get(url, params=None):
             status_code = f.status if hasattr(f, "status") else f.getcode()
             if status_code == 200:
                 data = f.read().decode("utf-8")
-                json.loads(data)  # Validate JSON string.
+                _ = json.loads(data)  # Validate JSON string.
                 return data
             logger.error(status_code)
             return "{}"